This invention relates to an ink feeding apparatus for an offset printing press which uses highly viscous ink for printing.
In commonly accepted technique of the offset printing press using highly viscous ink, an operator feeds ink by hand with a few exceptions. Otherwise, due to the recent automatization, an automatic system has been employed in a part of the field which uses a pump for feeding ink. In this pump system, ink is fed by the pump from an ink tank to a printing press through a pipe line. However, a web type offset printing press uses a highly viscous ink which is accompanied with the well known thixotropic phenomenon, and furthermore it is required to be able to feed ink little by little continuously because the common usage of ink is for a considerably small rate, for example, at one or two liters per hour. Thus, this system with pump includes the following disadvantages.
Namely, during operation of the printing press, the ink is held at a suitable viscosity for printing by pressurization as well as by the simultaneous agitation thereof by means of the pump. However when the pump is stopped, upon stopping an operation of the printing press, which ends the ink feeding, then the ink contained in the pipe line returns to the original highly viscous liquid again. This causes a difficulty in feeding the ink for the next operation, because the conventional prior art employs a pump larger than required for incessant circulation of ink, and also the thixotrophic phenomenon of ink is delayed most at the end of the pipe line in the printing press. When ink in this portion becomes a soft viscous liquid, there the so called "dropping", i.e. "droplet falling" phenomenon occurs in which an amount of ink drops or is poured out intermittently. Therefore, control of the flow rate of the ink is required, which flow rate control is difficult to achieve. Therefor in the case of an offset printing press which requires a continuous feeding of ink little by little as described, this pump system is not adequate. Furthermore, with respect to an offset printing press, an ink receiver used therein should be washed out whenever a coloured pattern is changed. Accordingly, the pump system which is necessarily accompanied with the "droplet falling" phenomenon cause a large loss of ink. This disadvantage is based on the fact that only a pump serves to pressurize and to agitate ink in the pipe line used for ink feeding.